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Quantum chromodynamics and colour singlet exchange in high energy interactions
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Nuclear and Particle Physics.
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Quantum chromodynamics (QCD) is the fundamental theory in elementary particle physics that describes the strong interaction in terms of exchanges of force-carrying, colour-charged particles known as gluons. Although well-established through experimental verifications, there are fundamental unsolved problems in the theory.

In this thesis, some novel aspects of strong interaction dynamics are studied in the context of colour singlet exchange processes — interactions where complex systems of gluons with no net colour charge are exchanged. Both perturbative and non-perturbative QCD methods are used, as well as Monte Carlo computer simulations.

Soft colour interactions in the final state of a high energy collision can lead to effective colour singlet exchange. Non-perturbative models for such interactions are shown to give a good description of diffractive production of W, Z, bb, J/ψ and jets in pp collisions at the Tevatron. Predictions are given for diffractive Higgs boson and prompt photon production at hadron colliders.

Rapidity gaps between jets is a new phenomenon which is studied with an improved perturbative calculation of hard colour singlet exchange using the BFKL equation, taking into account previously neglected contributions and non-leading logarithmic corrections. Including also underlying soft rescattering effects, the complete model reproduces well data from the Tevatron.

Diffractive vector meson production through hard colour singlet exchange in γp collisions is studied in the framework of the conformal invariant non-forward solution of the BFKL equation. Expressions for helicity-dependent amplitudes are derived, and the results show good agreement with data on J/ψ and ρ production from the ep collider HERA.

These studies lead to a deeper knowledge of complex gluon dynamics, and therefore advance our understanding of QCD.

Abstract [sv]

X

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2003. , p. 75
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 829
Keywords [en]
Physics
Keywords [sv]
Fysik
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:uu:diva-3385ISBN: 91-554-5598-0 (print)OAI: oai:DiVA.org:uu-3385DiVA, id: diva2:162600
Public defence
2003-05-16, the Polhem lecture hall (10134), Ångström laboratory, Uppsala, 10:15
Opponent
Supervisors
Available from: 2003-04-15 Created: 2003-04-15 Last updated: 2012-03-12Bibliographically approved
List of papers
1. Rapidity gaps at HERA and the Tevatron from soft colour exchanges
Open this publication in new window or tab >>Rapidity gaps at HERA and the Tevatron from soft colour exchanges
2000 (English)In: Journal of Physics G: Nuclear and Particle Physics, ISSN 0954-3899, E-ISSN 1361-6471, Vol. 26, p. 712-715Article in journal (Refereed) Published
Abstract [en]

Models based on soft colour exchanges to rearrange colour strings in the final state provide a general framework for both diffractive and non-diffractive events in ep and hadron-hadron collisions. We study two such models and find that they can reproduce rapidity gap data from both HERA and the Tevatron. We also discuss the influence of parton cascades and multiple interactions on the results.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-90286 (URN)10.1088/0954-3899/26/5/332 (DOI)
Available from: 2003-04-15 Created: 2003-04-15 Last updated: 2017-12-14Bibliographically approved
2. Soft color interactions and diffractive hard scattering at the Fermilab Tevatron
Open this publication in new window or tab >>Soft color interactions and diffractive hard scattering at the Fermilab Tevatron
2001 (English)In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 64, no 11, p. 114015-Article in journal (Refereed) Published
Abstract [en]

An improved understanding of nonperturbative QCD can be obtained by the recently developed soft color interaction models. Their essence is the variation of color string-field topologies, giving a unified description of final states in high energy interactions, e.g., diffractive and nondiffractive events in ep and pp̅ . Here we present a detailed study of such models (the soft color interaction model and the generalized area law model) applied to pp̅ , considering also the general problem of the underlying event including beam particle remnants. With models tuned to DESY HERA ep data, we find a good description also of Fermilab Tevatron data on production of W, beauty and jets in diffractive events defined either by leading antiprotons or by one or two rapidity gaps in the forward or backward regions. We also give predictions for diffractive J/ψ production where the soft exchange mechanism produces both a gap and a color singlet cc̅ state in the same event. This soft color interaction approach is also compared with Pomeron-based models for diffraction, and some possibilities to experimentally discriminate between these different approaches are discussed.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-90287 (URN)10.1103/PhysRevD.64.114015 (DOI)
Available from: 2003-04-15 Created: 2003-04-15 Last updated: 2017-12-14Bibliographically approved
3. Diffractive Higgs Boson Production at the Fermilab Tevatron and the CERN Large Hadron Collider
Open this publication in new window or tab >>Diffractive Higgs Boson Production at the Fermilab Tevatron and the CERN Large Hadron Collider
2002 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 89, no 8, p. 081801-Article in journal (Refereed) Published
Abstract [en]

Improved possibilities to find the Higgs boson in diffractive events, having less hadronic activity, depend on whether the cross section is large enough. Based on the soft color interaction models that successfully describe diffractive hard scattering at DESY HERA and the Fermilab Tevatron, we find that only a few diffractive Higgs events may be produced at the Tevatron, but we predict a substantial rate at the CERN Large Hadron Collider.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-90288 (URN)10.1103/PhysRevLett.89.081801 (DOI)
Available from: 2003-04-15 Created: 2003-04-15 Last updated: 2017-12-14Bibliographically approved
4. Diffractive Higgs bosons and prompt photons at hadron colliders
Open this publication in new window or tab >>Diffractive Higgs bosons and prompt photons at hadron colliders
2003 (English)In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 67, p. 011301-Article in journal (Refereed) Published
Abstract [en]

Models for soft color interactions have been successful in describing and predicting diffractive hard scattering processes in ep collisions at DESY HERA and pp̅ at the Fermilab Tevatron. Here we present new comparisons of the model to recent diffractive dijet data, also showing good agreement. The topical issue of diffractive Higgs boson production at the Tevatron and CERN LHC hadron colliders is further investigated. For H⃗γγ the irreducible background of prompt photon pairs from qq̅ →γγ and gg⃗γγ is always dominating, implying that higher branching ratio decay modes of the Higgs boson have to be used. However, such prompt photons can be used to test the basic prediction for Higgs boson production since gg⃗γγ involves a quark loop diagram similar to gg⃗H.

National Category
Subatomic Physics
Research subject
Physics with specialization in Elementary Particle Physics
Identifiers
urn:nbn:se:uu:diva-90289 (URN)10.1103/PhysRevD.67.011301 (DOI)
Available from: 2003-04-15 Created: 2003-04-15 Last updated: 2017-12-14Bibliographically approved
5. Hard colour singlet exchange at the Tevatron from the BFKL equation
Open this publication in new window or tab >>Hard colour singlet exchange at the Tevatron from the BFKL equation
2002 In: Deep Inelastic Scattering. DIS 2001 Proceedings of the 9th International Workshop, 2002, p. 820-823Chapter in book (Other academic)
Identifiers
urn:nbn:se:uu:diva-90290 (URN)981-02-4754-0 (ISBN)
Available from: 2003-04-15 Created: 2003-04-15 Last updated: 2011-11-11
6. HARDCOL: Hard Colour Singlet exchange processes in PYTHIA
Open this publication in new window or tab >>HARDCOL: Hard Colour Singlet exchange processes in PYTHIA
Manuscript (Other academic)
Identifiers
urn:nbn:se:uu:diva-90291 (URN)
Available from: 2003-04-15 Created: 2003-04-15 Last updated: 2011-11-11
7. Hard colour singlet exchange and gaps between jets at the Tevatron
Open this publication in new window or tab >>Hard colour singlet exchange and gaps between jets at the Tevatron
2002 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 524, no 3-4, p. 273-282Article in journal (Refereed) Published
Abstract [en]

The new kind of events with a rapidity gap between two high-ET jets, observed in high energy  collisions at the Tevatron, is found to be well described by the exchange of a colour singlet gluon system in the BFKL framework. This requires going beyond the conventional asymptotic Mueller–Tang approximation, which results in qualitatively different features of the basic parton–parton scattering amplitude. Non-leading corrections to the BFKL equation are included by incorporation of the consistency constraint and the running QCD coupling. Hadronisation and other non-perturbative QCD effects are treated through a complete Monte Carlo simulation, providing a gap survival probability that varies event-by-event, facilitating comparison with experimental results.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-90292 (URN)10.1016/S0370-2693(01)01379-X (DOI)
Available from: 2003-04-15 Created: 2003-04-15 Last updated: 2017-12-14Bibliographically approved
8. Diffractive heavy vector meson production from the BFKL equation
Open this publication in new window or tab >>Diffractive heavy vector meson production from the BFKL equation
2002 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 26, no 2, p. 219-228Article in journal (Refereed) Published
Abstract [en]

Diffractive heavy vector meson photoproduction accompanied by proton dissociation is studied for arbitrary momentum transfer. The process is described by the non-forward BFKL equation, for which a complete analytical solution is found, giving the scattering amplitude. The impact of non-leading corrections to the BFKL equation is also analysed. Results are compared to the HERA data on production.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-45268 (URN)10.1140/epjc/s2002-01056-7 (DOI)
Available from: 2006-09-26 Created: 2006-09-26 Last updated: 2017-12-05Bibliographically approved
9. Diffractive vector mesons at large momentum transfer from the BFKL equation
Open this publication in new window or tab >>Diffractive vector mesons at large momentum transfer from the BFKL equation
2002 (English)In: Acta Physica Polonica B, ISSN 0587-4254, E-ISSN 1509-5770, Vol. 33, no 11, p. 3511-3516Article in journal (Refereed) Published
Abstract [en]

Diffractive vector meson photoproduction accompanied by proton dissociation is studied for large momentum transfer. The process is described by the non-forward BFKL equation, for which an analytical solution is found for all conformal spins, giving the scattering amplitude. Results are compared to HERA data on \rho production.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-90294 (URN)
Available from: 2003-04-15 Created: 2003-04-15 Last updated: 2017-12-14Bibliographically approved
10. Vector Meson Photoproduction from the BFKL Equation I: Theory
Open this publication in new window or tab >>Vector Meson Photoproduction from the BFKL Equation I: Theory
2003 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 9, p. 008-Article in journal (Refereed) Published
National Category
Subatomic Physics
Research subject
Physics with specialization in Elementary Particle Physics
Identifiers
urn:nbn:se:uu:diva-48593 (URN)10.1088/1126-6708/2003/09/008 (DOI)
Available from: 2008-10-17 Created: 2008-10-17 Last updated: 2017-12-05Bibliographically approved

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Output format
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